Posted
by
timothyon Thursday April 02, 2009 @05:00PM
from the phrase-your-answer-in-wine-review-terms dept.

CNETNate writes "A new video simulation developed by Andrew Hamilton and Gavin Polhemus of the University of Colorado, Boulder, on New Scientist today, shows what you might see on your way towards a black hole's crushing central singularity. Hamilton and Polhemus built a computer code based on the equations of Einstein's general theory of relativity, and the video produced allows the viewer to follow the fate of an imaginary observer on an orbit that swoops down into a giant black hole weighing 5 million times the mass of the sun, about the same size as the hole in the centre of our galaxy. The research could help physicists understand the apparently paradoxical fate of matter and energy in a black hole."

You'd only gt that black-on-black view if you were falling into a black hole in a ship specially decorated for Hotblack Desiato. Come to think of it, that would be highly appropriate under the circumstances.

Maybe you'd interpret it as black space, but technically you would not see anything there since its gravity is too strong to let any light out and your eyes rely on reflected light off an object to see it. You would see light bent around the hole, and as you approached the hole this light would get more and more distorted, especially at the event horizon (at least according to the general relativity theory the sim was based on).

So basically, if you're staring directly at the hole, you'd see nothing (it wou

Getting first post on Slashdot while falling into a black hole.Cynical phycisists might call that an extremely slow news day.Other physicists might remark that now there are 2 things which can escape from a black hole: Hawking radiation and Slashdot posts.

I'm talking 'observer' in the theoretical sense, although as others pointed out elsewhere on this discussion, supermassive (center-of-galaxy class) black holes are big enough that at the event horizon the gravity gradient is still pretty small, definitely small enough to be survivable by a human in a ship.

So you could in theory observe all that freaky shit happening as you approach the event horizon. Then again you'd have somewhat of a hard time telling anyone outside the black hole about it...

...and a finite circumference. An observer falling towards the singularity would feel the local gradient in the gravitational field increase as they fall, probably to the point where staying in one piece becomes a challenge. This would go on for a long time from their POV.

so what about Hawking radiation? For the outsider observer, an unfed black hole is continually shrinking (albeit slowly) while the subject falls very slowly into it. So wouldn't the (very long living) observer see the black hole shrink faster than the subject falls into it? But the subject must also come to the same conclusion, and so see the black hole shrink very rapidly as he approached it.

I expect (but am not going to do the math) that everything works out once you include the idea that if the event horizon is retreating (the hole is shrinking) then the time dilation effect is also not constant for a particular distance from the centre of the hole.

Imagine an observer A who is falling towards a black hole at just the right speed to maintain position a certain distance from the event horizon. From the point of view of an outsider, B, because the event horizon is shrinking, A is approaching th

I always thought that if you could see the outside universe as you were falling in the outside would appear to be moving faster and faster (from an inside perspective) the closer you got towards the center of the singularity. (effectively skipping ahead into the future faster and faster)

since quite a lot of junk falls into a black hole especially over the period of the universe's lifetime, you'd probably see all sorts of large amounts of crap following in behind you at a tremendous speed (stars etc) until it got close enough to be affected by the same space time distortion, but never quite catching up to your point

from an outside perspective if you could see what was happening beyond the event horizon, the stuff falling in would appear to move slower and slower the closer it got towards the center never quite reaching the center point
which makes me wonder if someone falling into one of these things would actually reach the end of time itself a lot more quickly than everyone else on the outside (assuming there is such a thing)

I think you're right. I remember reading that there is no indication that you've crossed the event horizon and nothing appears to have happened, while to an observer, you'll slowly descend to the center yet never reach it, just like you said. The things happening in the video don't really make sense from what I've learned.

Time frames will approach infinity from the viewpoint of the external observer, as dictated by special relativity.

The big question is what exactly happens at the surface and inside a black hole. And it depends on what exactly the nature of space and time are, and how they fail.

We can make conjectures here, but the idea that there is something space-shattering happening there seems rather likely. The idea that a macro-figure Calabi-Yau shape that prevents the collapse past the event horizon seems probable, b

Nothing exciting happens at the event horizon. It's just the point at which you need infinite energy to leave the black hole's event horizon again. For very large black holes, such as that in the center of the Milky Way, a human can safely pass the event horizon and see what it looks like inside. Eventually, however, the human will be subjected to higher and higher tidal forces--but that has to do with the size of the black hole, not with the crossing of an event horizon.

I thought exciting things DID happen at the surface, namely the particle zoo that the quantum foam "contains". And if the entropy calculations are correct (which im sure they are), I'd like data on those perpendicular X-ray jets.

The previous poster is right; there is no local experiment you can perform at the horizon to determine whether you're at the horizon. You can see a lot of radiation if you hover at the horizon, but that's because you're expending energy to hover. Polar X-ray jets have nothing to do with the horizon, "quantum foam", Hawking radiation, or black hole entropy: they're due to matter and magnetic fields outside of the black hole.

It's hard to define "radius" in a Schwarzschild spacetime. Outside and up to the event horizon, the radial coordinate is defined indirectly by the surface area of a sphere, which is sqrt(area/4pi) and is finite. (The circumference is also finite.) However, the proper distance between points at two different radii is not equal to the difference of their radial coordinates.

Inside a black hole, you can't even define a radius this way, because spacetime inside the horizon is no longer static, and there's no

About the same as it feels to be a bug hitting an Audi windscreen on the Autobahn... when you've been stretched to several hundred times your original length, you're most likely no longer capable of observing anything, so it looks pretty much like nothingness. Can a soul escape from the event horizon of a black hole, or is it doomed to spend forever in purgatory inside the black hole? And is that better or worse than being stuck in New Jersey?

Olber's Paradox says that the sky should be infinitely bright in all directions. In a black hole, this might actually be the case, as there's nothing to obstruct the view and nowhere else for the photons to go.

If you were falling into a black hole, I think it would be far more interesting to do so while facing away from the hole, as this would theoretically (according to relativity) allow you to witness the remaining life of the universe played out at a greatly accelerated rate.

Falling into a black hole does not allow you to see the end of the universe [nasa.gov]. (The FAQ I linked to discusses one case in which a perfectly symmetric, rotating vacuum black hole does experience infinite blueshift, but the existence of matter or quantum gravity effects very likely destroy that property of the black hole.)

Considering that a black hole is more massive than the sun, then it will take longer to fall into the black hole than for the earth to fall into the sun and the sun will go nova before the simulation ends...

You're quite correct that making a video and sending a probe are two entirely different things. I somehow doubt that the video took a few hundred million to make, while still providing a potentially useful visualization of something that I somehow doubt we'll witness first hand.

1. Reaching a black hole is not impossible with current technology, but it is beside the point.

2. This is a research tool intended to help physicists understand what happens to matter as it enters a black hole.

3. Using all your grant money to run on an SGI cluster is so... 1990s. This was probably rendered on a modern laptop. If the calculations really did turn out to be too computationally intensive for a modern personal computer (I wouldn't count on it), they would have bought time on one of the more modern Linux or Mac computing clusters.

4. "Cool" is not the purpose. If it was, there wouldn't be fun guide-lines left in the film. This is a research tool that happened to get passed on to NewScientist to share with anyone who might be interested.

I can report with certainty that this was rendered (or at least CAN be rendered) on a modern laptop; I attended Professor Hamilton's course on Black Holes in which he used the Black Hole Simulator. It ran at this quality in real-time (including changing angles, time dilation, and different types of black holes) on a 2005 Alienware laptop running Gentoo.

Reaching a black hole is not impossible with current technology, but it is beside the point.

Yes it is. It would take millennia if not millions of years to reach the closest black hole with current technology. We can't build anything that would be able to power itself for that long, nevermind that humanity would most likely be extinct by the time we reached it.

Well, good thing then that we're working on building our own locally. Anyone care for spaghetti?

Spaghettification. Let me guess. I can see only two options: one -- due to the bizarre effects of the intense gravitational pull, and because we're entering a region of time and space where the laws of physics no longer apply, we all of us inexplicably develop an irresistible urge to consume vast amounts of a certain wheat-based Italian noodle conventionally served with Parmesan cheese; or two -- we, the crew, get turned into spaghetti. I have a feeling we can eliminate option one.

Once you came near the event horizon (given current technology) you would more than likely be dead, so this is a pretty pointless video...

Pointless unless you've studied relativistic physics, in which case the video is a modernized version of the classic thought experiment "Einstein's Train." [syr.edu]. Everyone involved would be pretty dead if the train was moving at speeds fast enough to introduce relativistic effects perceptable by the ordinary senses, yet the illustration aids in an understanding of the physics.

The article is quite clear:

That's where visualisations like this might just help. "Close to the singularity, it appears that the entire three-dimensional universe is being crushed into a two-dimensional surface," says Hamilton (see Our world may be a giant hologram). But whether it hints that a 2D view is more fundamental is not yet clear. "Does it have any profound significance? I don't know..."

The death of the hypothetical observer is irrelevant to the usefulness of the video.

Speed does not kill, acceleration does. If you accelerate the "train" at 1g, it would take only one year to reach about 0.77c, more than enough to see relativistic effects.

An anonymous comment that relies upon particular assumptions that are forbidden by the nature of the scenario. Like a train traveling through a vacuum, so that the train isn't destroyed by atmospheric resistance and the external observer isn't killed by the shockwave -- but the vacuum can conduct lightning. Like a train traveling in a

"A code" in the lingo of the scientific programming community means "a computer program that simulates these equations in an expedient manner," i.e. there is more than one way to discretize and program the solution of the equations, but they have done it in one specific way. It is therefore "a computer code."